1. Field of the Invention
The present invention relates to a method for forming a self-aligned contact hole and a semiconductor device having a self-aligned contact hole.
2. Description of Related Art
In conventional semiconductor devices, a number of contact holes have been formed in a self-aligned manner by utilizing a pattern of an isolating field insulator layer. In DRAMs (dynamic random access memory) of a stacked capacitor one-transistor type, for example, the contact holes have been formed in the self-aligned manner by utilizing an isolating field insulator layer and insulator layers that are formed on an upper surface and a side wall surface of a word line. However, this self-aligned contact hole forming method has been disadvantageous in the following points:
First, for formation of self-aligned contact holes, the isolating field insulator layer had to be formed to have a sectional view configuration or shape that has small bird's beaks and steep steps at edges of an isolating field insulator layer pattern. In addition, the isolating field insulator layer had to have a thickness which larger than that which is necessary and sufficient for an inherent device isolation. This becomes a direct cause that greatly lowers working precision of photoresist patternings and etchings in succeeding photolithographic processes.
In addition, since it is necessary to previously form the insulator layer on the upper surface of the word line, a step formed by the word line has inevitably become large. Here, for example, assume that a thickness of the word line is 0.3 .mu.m, the thickness of the insulator layer formed on the upper surface of the word line is 0.2 .mu.m, and the thickness of the insulator layer formed on the side wall surface of the word line is 0.2 .mu.m. In this case, assuming that a spacing between each pair of adjacent word lines is 0.7 .mu.m in a mask layout pattern, a slit-like concave or groove having a width of 0.3 .mu.m and a depth of 0.5 .mu.m will be formed. This makes the photoresist patternings and the etchings in succeeding photolithographic processes very difficult
As mentioned above, if the self-aligned contact holes are formed in the prior art method as mentioned above, the step of the underlying pattern is very large, and the working precision of the succeeding photolithographic processes is remarkable decreased. As a result, the prior an method of the self-aligned contact hole formation could be hardly used in practice.
In addition, since the isolating field insulator layer is utilized for formation of the self-aligned contact holes, the prior art method could be applied to only formation of the self-aligned contact holes on a silicon substrate.